The present invention relates to an optical exposure apparatus, and, more particularly, to an optical exposure apparatus which is suitable for optically forming a predetermined pattern on an exposed surface such as a semiconductor wafer.
An optical exposure apparatus includes a means for irradiating a pattern with light, means for directing light obtained from the pattern onto surface being exposed so that an image of the pattern is formed on the surface, and means for moving the surface being exposed so that the exposure position on the surface is changed.
To precisely form an image of the pattern on the surface being exposed, it is necessary to effect focusing so that the image of the pattern is correctly formed on the surface being exposed. An apparatus for effecting forcusing includes means for detecting any deviation from a predetermined reference in the distance between the surface being exposed and the means for directing light, and means for moving the surface to compensate for that deviation. The means for detecting the deviation often has gas-delivering hole through which a gas is emitted toward to the surface being exposed, and means for detecting any change in the gas flow rate through the gas-delivering hole due to the deviation.
However, an axis of the gas-delivering hole is usually aligned with the optical axis of the light directed onto the surface being exposed. Therefore, the gas-delivering hole must be large enough so that it does not hinder the light travelling along the optical axis. Therefore, an increased exposure surface is inevitably required so that any change in the gas flow rate through the gas-delivering hole due to deviation in the distance between the surface being exposed and the light-directing means, from a predetermined reference can be detected. This means that wide, useless regions which are not exposed must be provided around the periphery of the surface being exposed.
One object of the present invention is to provide an optical exposure apparatus which is suitable for preventing the formation of a wide, useless region which will not be exposed, around the peripheral edge of the surface being exposed.
Another object of the present invention is to provide an optical exposure apparatus which is suitable for obtaining a high production rate.
According to the present invention, a pattern is irradiated with light, and light obtained from the pattern is then directed onto the surface being exposed, so that an image of the pattern is formed on the surface. The surface is moved so that the exposure position can be changed.
Provision is made of means for detecting any deviation from a predetermined reference in the distance between the surface being exposed and the light-directing means, and means which moves the surface being exposed so as to compensate for such deviation. The detection means includes means in which a plurality of gas-delivering holes are provided around the optical axis of the light directed onto the surface being exposed, the gas being emitted toward different positions on the surface being exposed, and means for detecting any change in the gas flow rate through the plurality of gas-delivering holes due to a deviation from the predetermined reference in the distances between different positions on the surface being exposed and the light-directing means.